1. Field of the Invention
The present invention relates to authentication processing of a relay apparatus, a transmitting apparatus, and a receiving apparatus.
2. Description of the Related Art
In recent years, a form in which a transmitting apparatus (hereinafter, referred to as a source device) such as a DVD player and a Blu-ray (registered trademark, hereinafter, referred to as Blu-ray) and a receiving apparatus (hereinafter, referred to as a sink device) such as a TV set are connected via a relay device (hereinafter, referred to as a repeater) such as an AV amplifier by using an HDMI (High-Definition Multimedia Interface) cable is in widespread use. By using the HDMI cable, video and audio data from a source device can be transmitted and received in digital format in high image quality and sound quality. Also, device authentication and content protection specified by the HDCP (High-bandwidth Digital Content Protection) standard are used as functions to protect copyrights of content transmitted from a source device.
By using the HDCP standard, content data between a source device and a repeater and between the repeater and a sink device can be encrypted. According to the HDCP standard, the source device and the repeater, and the repeater and the sink device each perform HDCP authentication by using an authentication protocol. In the HDCP authentication, first authentication, second authentication, and third authentication are performed. If, as a result of the HDCP authentication, the repeater and the sink device are not determined to be invalid devices, the repeater and the sink device can decrypt content encrypted by the source device. Device authentication in the HDCP standard is performed by using a DDC (Display Data Channel) communication line.
Incidentally, a source device and a repeater may not be able to complete HDCP authentication normally even if the timing of transmitting/receiving a signal specified in an authentication sequence of the HDCP standard is met. If, for example, the repeater transmits a TMDS (Transition Minimized Differential Signaling) signal to a sink device and then, immediately thereafter transmits an HDCP authentication start signal to the sink device, the sink device receives the HDCP authentication start signal before locking the TMDS signal and so may not be able to start HDCP authentication processing normally. Locking a TMDS signal means detecting the TMDS signal and analyzing the resolution and the like of the TMDS signal. When starting HDCP authentication, some source devices switch and transmit TMDS signals in different resolutions to the repeater in a short time. Accordingly, the repeater transmits TMDS signals received from the source device to the sink device and thus, TMDS signals in different resolutions are transmitted from the repeater to the sink device a plurality of times in a short time. As a result, the sink device cannot lock TMDS signals normally and cannot perform HDCP authentication normally. Further, the repeater transmits an instruction of HDCP first authentication to the sink device and then requests a key to determine whether the HDCP first authentication is completed normally, but if the interval between the start instruction of the HDCP first authentication and the instruction of key request is not appropriate, the verification of the key may fail. Further, if the time between verification processing of the key and the start of encryption of the TMDS signal is not appropriate, the repeater may fail to encrypt the TMDS signal.